Dimpled thermal processing furnace tube

ABSTRACT

A tube for use in a thermal processing furnace. The tube comprises an elongated cylindrical tube having an inner surface with a plurality of dimples disposed thereon. In one preferred version of the invention, the dimples are formed as an integral part of the inner surface of the cylindrical tube. In another aspect of the invention, the dimpled furnace tube is incorporated into a thermal processing furnace. In this aspect of the invention, the furnace includes a furnace tube having an inner surface describing an elongated cylindrical heated chamber for receiving and processing a plurality of axially aligned spaced apart semiconductor wafers. The inner surface has a plurality of dimples disposed thereon. The furnace further includes an inlet for introducing reactant and/or inert gases into one end of the cylindrical chamber to flow axially within the chamber by the wafers and an outlet for removing the gases from the cylindrical chamber.

FIELD OF THE INVENTION

The invention relates generally to semiconductor processing equipmentand, more particularly, to a thermal processing furnace tube.

BACKGROUND OF THE INVENTION

Semiconductor devices are constructed of patterned layers ofelectrically conductive, non-conductive and semi-conductive materialsstacked over a silicon wafer. The layers of material are successivelydeposited on the wafer and etched into predefined patterns to formindividual component structures within the particular device beingfabricated. The manufacturing process typically also includes the heattreatment of the silicon wafers at different stages of manufacture in athermal processing furnace, sometimes referred to as a "diffusion"furnace. Diffusion furnaces are used for heat treatment processes suchas impurity diffusion, oxide growth, chemical vapor deposition ("CVD"),annealing and the like. The furnaces basically include a furnace tubesurrounded by a heating element. The wafers are placed in the furnacetube in specially made cassettes or "boats" wherein the wafers arearranged parallel to one another and oriented so that the surface ofeach wafer is perpendicular to the longitudinal axis of the furnacetube. The diameter of the furnace tube is somewhat greater than thediameter of the wafers.

During processing, the wafers are heated to the desired temperature andinert and reactant gases are introduced into the furnace tube. Gasesintroduced into one end of the furnace tube thus flow over the wafersaxially along the length of the furnace tube and are exhausted at theother end. A region of laminar flow exists between transition areasformed by velocity gradients in the gases flowing axially along theinner surface of the tube and along the edges of the wafers. A region ofturbulent flow exists fully across the surfaces of the wafers. Thisturbulent region and the corresponding pressure drop promotes a moreuniform reaction between the gases and the surface materials of thewafers. The present invention is directed to an improved furnace tubewherein the transition area formed along the inner surface of the tubeis extended outward to narrow the laminar region of the flow of gasesthrough the tube. Narrowing the laminar region of flow causes higherturbulence in the turbulent region, which increases the pressure dropacross the surface of the wafers, and results in a more uniform reactionacross the surface of the wafers.

SUMMARY OF THE INVENTION

Accordingly, it is one object of the invention to enhance the uniformityof the reaction between the gases introduced into the furnace tube andthe surface materials of the wafers. It is another object to extend thetransition area formed along the inner surface of the furnace tubeoutward to narrow the laminar region of the flow of gases through thetube and thereby increase the pressure drop across the surface of thewafers to promote a more uniform reaction across the surface of thewafers.

These and other objects are achieved by a furnace tube that includes anelongated cylindrical tube having an inner surface with a plurality ofdimples disposed thereon. In one preferred version of the invention, thedimples are formed as an integral part of the inner surface of thecylindrical tube. In another aspect of the invention, the dimpledfurnace tube is incorporated into a thermal processing furnace. In thisaspect of the invention, the furnace includes a furnace tube having aninner surface describing an elongated cylindrical heated chamber forreceiving and processing a plurality of axially aligned spaced apartsemiconductor wafers. The inner surface has a plurality of dimplesdisposed thereon. The furnace further includes an inlet for introducingreactant and/or inert gases into one end of the cylindrical chamber toflow axially within the chamber by the wafers and an outlet for removingthe gases from the cylindrical chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 cross section side view of a conventional thermal processingfurnace.

FIG. 2 is a cross section side view of a thermal furnace processing tubehaving a dimpled inner surface.

FIG. 3 is a cut-away perspective view of a thermal furnace processingtube showing the dimpled inner surface.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-3, a furnace 10 for thermal processing ofsemiconductor wafers is illustrated according to the preferredembodiment of the invention. An elongated cylindrical furnace tube 12 islocated inside a cylindrical opening 14 in the walls 16 of furnace 10.Support collars 18 support furnace tube 12 and serve as a gasket orpacking gland to seal opening 14. Furnace 10 includes resistance typeheater element 20 which is used to raise the temperature within thefurnace tube 12 for performing certain steps in the semiconductormanufacturing process, such as diffusion, CVD, oxide growth or the like.Walls 16, collars 18 and furnace tube 12 are typically made of aceraminc or refractory material such as quartz or silicon carbide. Asource of reactant and/or inert gas is connected to an inlet 22 at oneend of furnace tube 12 to provide the desired atmosphere within tube atvarious times in the operating cycle. Since the apparatus is intended toaccommodate 8 inch wafers, furnace tube 12 has a diameter of about 12inches, although the particular size is selected according to theintended use of the furnace. Furnace 10, as just described, is intendedto represent any conventional tubular diffusion furnace commonly used insemiconductor manufacturing. The construction and operation of suchfurnaces are well known to those skilled in the art.

Dimples 24 are formed on inner surface 25 of furnace tube 12, as shownin FIGS. 2 and 3. Dimples 24 extend the transition area 23 formed alonginner surface 25 of tube 12 outward to narrow the laminar region 27 ofthe flow of gases through tube 12. Narrowing the laminar region 27 offlow causes higher turbulence in the turbulent region 28, whichincreases the pressure drop across the surface of the wafers 30, andresults in a more uniform reaction across the surface of the wafers.Dimples 24 are preferably formed as an integral part of inner surface 25of furnace tube 12. Dimples 24, as used herein, represent generally anytopographic feature disposed on inner surface 25 of tube 12 to extendtransition area 23. For example, a variety of projections, bumps and/orindentations could be used. The preferred size, shape and spacing ofdimples 24 may be varied to achieve the desired flow regions within tube12 depending on the processing temperatures, types of gases used, totalgas flow and wafer spacing.

Wafers 30, which are typically carried in a cassette or "boat", areplaced on paddle 32 and inserted into furnace tube 12. As is well knownto those skilled in the art, a variety of different conventional waferloading devices may be used to insert the wafers into and remove themfrom furnace tube. The type of insertion mechanism used is not importantto the invention, except to the extent a covered insertion tube is usedsuch as that described in U.S. Pat. Nos. 4,526,534 and 5,256,060, issuedto Wollmann and Philipossian et al., respectively. Where a covered innertube such as that disclosed in the Wollmann and Philipossian patents isused, the inner surface of the inner tube should be dimpled as describedabove to achieve the enhanced flow across the surface of the wafers.Then, wafers 30 are elevated to the desired temperature and reactantgases are introduced into furnace tube 12. The gas flows over wafers 30,as indicated by arrows 34 in FIG. 2, for the desired time after whichthe reactant gases are exhausted from furnace tube 12 and replaced withan inert gas. The wafers 30 are then removed from furnace tube 12 forfurther processing. Baffles 36 are typically used to retard heat lossand to help ensure adequate reactant gas mixing without undulyrestricting the flow of gas through furnace tube 12. Many differentbaffle arrangements are known and can be substituted for the one shown.The spent or exhaust gases are typically collected in a scavenger boxfor delivery to a "scrubber" or other suitable waste disposal orrecycling system (not shown) through outlet 40.

There has been shown and described a novel thermal processing furnacetube which has a dimpled inner surface to create a more uniform reactionacross the surface of the wafers. The particular embodiments shown inthe drawings and described herein are for purposes of example and shouldnot be construed to limit the invention as set forth in the appendedclaims.

I claim:
 1. A thermal processing furnace, comprising:a. a furnace tubehaving an inner surface describing an elongated cylindrical chamber forreceiving and processing a plurality of axially aligned spaced apartsemiconductor wafers, the inner surface having a plurality of dimplesdisposed thereon; b. an inlet for introducing reactant and/or inertgases into one end of the cylindrical chamber to flow axially within thechamber by the wafers; and c. an outlet for removing the gases from thecylindrical chamber.
 2. A furnace according to claim 1, wherein thedimples are formed as an integral part of the inner surface of thefurnace tube.
 3. A tube according to claim 1, wherein the dimplescomprise indentations formed in the inner surface of the tube.
 4. A tubeaccording to claim 1, wherein the dimples comprise bumps formed on theinner surface of the tube.